Interleukin‐10 inhibits the induction of monocyte procoagulant activity by bacterial lipopolysaccharide

Abstract

Monocytes stimulated with bacterial lipopolysaccharide (LPS) generate a procoagulant activity (PCA) related to the induction of tissue factor (TF) expression at their surface. Since interleukin‐10 (IL‐10) was recently shown to inhibit LPS‐induced cytokine production and is currently considered as a potential therapeutic agent in septic shock, we were interested to determine its effects on LPS‐induced monocyte PCA. Peripheral blood mononuclear cells (PBMC) from healthy donors were incubated with 1 μg/ml LPS in the presence of serial dilutions of recombinant human IL‐10 and PCA was determined after 6 h in a one‐stage clotting assay. IL‐10 inhibited in a dose‐dependent manner LPS‐induced TF‐dependent PCA: a significant effect was already observed with 30 pg/ml IL‐10 while 64–97% inhibition was achieved with 120 pg/ml IL‐10. In parallel flow cytometry experiments, IL‐10 was shown to block LPS‐induced TF expression at the surface of monocytes. In order to inhibit LPS‐induced PCA, IL‐10 had to be added to PBMC at least 6 h before LPS challenge. This inhibitory effect of IL‐10 was already apparent at the TF mRNA level and was prevented by co‐incubation with cycloheximide (20 μg/ml). These data suggest that IL‐10 acts via the induction of protein(s) which might interfer with TF gene transcription or mRNA stability. We conclude that the protective effects of IL‐10 in endotoxinemia might be related not only to cytokine synthesis blockade but also to inhibition of LPS‐induced PCA.